Systems and methods for interference cancellation

ABSTRACT

Systems and methods for interference cancellation in which a first signal having a first frequency may be cancelled with a second frequency having a second and different (e.g., lower) frequency by employing sampling to cancel the first signal with the separate signal at the sample instances.

This application is related in subject matter to concurrently filed U.S.patent application Ser. No. ______ (Attorney Docket LCOM-083), entitled“INTERFERENCE CANCELLATION FOR RECONFIGURABLE DIRECT RF BANDPASSSAMPLING INTERFERENCE CANCELLATION” by Fudge, which is herebyincorporated by reference in its entirety.

FIELD OF THE INVENTION

This invention relates generally to signal processing, and moreparticularly to interference cancellation.

BACKGROUND OF THE INVENTION

Loss of signal dynamic range is a problem commonly caused by stronginterferers in a radio frequency (RF) environment. Typical approachesemployed to address strong interferers include the use of fixed ortunable notch filters. Fixed notch filters can handle known RFinterferers, but cannot adapt to new interferers. Systems employingfixed notch filters must be re-designed and modified substantially ifthe fixed interference environment changes. Tunable notch filters, whileproviding more flexibility, suffer from lack of tuning resolution. Inparticular, tunable notch filters tend to have a constant quality factor(Q), which means that the notch bandwidth is proportional to the RFfrequency. Attempts at developing tunable notch filters with adequate Qhas been an active area of research for years and continues to be asignificant technical challenge. However, even if tunable notch filterscould meet the desired Q requirements, they still lack flexibility inthat they can only cancel a single interferer per notch. Employingmultiple notches essentially implies using multiple filters.

Another solution to addressing interference is to perform interferencecancellation. Spatial beamforming systems can use degrees of freedom tosteer spatial notches—this is the concept, for example, behind thegeneralized sidelobe canceller. However, these techniques do not applyto frequency cancellation and do not apply to single channel receiversin any case. Furthermore, even spatial beamformers may be susceptible todynamic range issues caused by strong interferers. The goal of activeinterference cancellation is to actively cancel the interference bydeveloping a cancellation signal, and in order to avoid problems causedby interference such as spurious signals and signal distortion, theinterference is cancelled early in the RF chain.

One solution to RF interference cancellation is to estimate theinterferer via a separate channel that is not in saturation, oradaptively while in saturation. An estimate of the interference is theninverted (or phase matched 180 degrees out of phase) and added to theinput. In such an architecture, interference signals may be heavilyattenuated in the cancellation path so that the interferer analog todigital converter (ADC) is not saturated. An adaptive filter block (orother digital signal processing (DSP) function), may then be used tofilter out all signals and noise other than the interference. Theinterference may then be amplified, phase inverted, and added to the RFinput. Time delay may be employed to allow cancellation of non-periodicsignals or non-periodic signal components. An example DSP adaptivefilter may consist of an analysis filter bank followed by thresholds oneach filter output with filter outputs below threshold being set to zeroand filter outputs above threshold being passed, followed by a synthesisfilter bank. The DSP would typically also include phase adjustments andpossibly additional phase matching based on monitoring of cancellationoutput. Reconstruction of a signal after ADC and up conversion issubject to imperfections introduced in the up conversion process and theneed to know the signal frequency and phase in order to coherentlycancel.

SUMMARY OF THE INVENTION

Disclosed herein are systems and methods that may be employed to provideinterference cancellation. Using the disclosed systems and methods, afirst signal having a first frequency may be cancelled with a secondfrequency having a second and different (e.g., lower) frequency byemploying sampling (e.g., pulse-based sampling or other wide bandwidthshort aperture sampling technique without hysteresis between samples) tocancel the first signal with the separate signal at the sampleinstances. The disclosed systems and methods may be implemented in oneembodiment with two sampling paths, a signal path and a cancel path. Thecancel path may be attenuated relative to the signal path to preventdistortion and saturation in the cancel path of interfering signals, andoptional time delay may be employed to allow cancellation ofnon-periodic signal components. In possible embodiments, the cancel pathmay include digital signal processing (DSP) implemented after an ADC, ormay include a tunable filter. In one embodiment, direct RF bandpasssampling may be employed in the signal and cancel paths, and folded (oraliased) intermediate frequency (IF) may be used to cancel RFinterference (i.e., rather than the same RF). In one embodiment, directRF interference cancellation may be employed for high RF input signalbands (e.g., from about 2 GHz to greater than about 40 GHz,alternatively from about 2 GHz to about 40 GHz, alternatively from about3 GHz to about 20 GHz).

Advantageously, the disclosed systems and methods may be applied todirect RF interference cancellation by using direct RF sampling on bothsignal path and cancellation path, without the need for up-conversion ofa cancellation signal from IF to RF. In this regard, traditional methodsof up-conversion, such as mixer-based solutions, are very sensitive toknowing the exact frequency of the RF interference and achieving theproper mixer phase to match the RF interference phase would be criticalto proper cancellation.

Thus, the disclosed systems and methods may be implemented to providecancellation of one frequency with a different frequency, and in oneembodiment to provide cancellation of a signal at one RF frequency withits folded IF version without up-conversion. Additionally, cancellationof an RF signal may be advantageously achieved without having to knowits exact frequency. The disclosed systems and methods may beimplemented with reconfigurable direct or Nyquist folding radiofrequency (RF) receivers to allow significantly improved dynamic range(e.g., improvements in dynamic range of 10 dB to 40+ dB) overconventional methods. In one exemplary embodiment, the disclosed systemsand methods may be implemented to improve the dynamic range of a Nyquistfolding receiver, e.g., to suppress a strong narrow-band interferingsignal by up to about 50 dB. The disclosed systems and methods may beimplemented (e.g., in electronic warfare (EW), electronic signalsintelligence (ELINT), electronic warfare support measures applications(ESM), etc.), for monitoring extremely wide bandwidths. For example, inone exemplary embodiment the disclosed systems and methods may beimplemented with a Nyquist folding receiver in an EW, ELINT, ESMapplication for monitoring bandwidths of from about 4 GHz up to about 20GHz or more) with low signal density. In another exemplary embodiment,the disclosed systems and methods may be implemented with a direct RFreceiver in a communications application for monitoring bandwidths downto about 10 MHz or less. In another exemplary embodiment, the disclosedsystems and methods may be implemented with a direct RF receiver in anEW, ELINT, ESM application for monitoring bandwidths of about 100 MHz toabout 1 GHz or more. It being understood that the foregoing bandwidthranges are exemplary only.

In one embodiment, the disclosed systems and methods may be implementedusing periodic pulse-based sampling, wide bandwidth short aperturesampling, or other sampling technique to cancel an RF input signal witha folded intermediate frequency (IF) version of the RF signal. In thisregard, an intermediate frequency (IF) version of the original RFinterference signal may be developed via bandpass sampling (e.g., at amuch lower frequency than the RF interference signal), and invertingthis IF signal to cancel the RF signal as part of a bandpass samplingprocess where the sampling is performed via pulse-based sampling. Insuch an embodiment, the RF signal does not need to be cancelled at alltimes, but instead only needs to be cancelled when sampling occurs(i.e., only at the sample times) since it does not matter what thesignal is doing between sample times. This is unlike conventionalcancellation, where the exact same frequency must be employed to cancelat all times in the presence of phase or frequency mis-match. Thus, inthe practice of the disclosed systems and methods, the frequency of theinterference does not need to be known since the RF signal is cancelledwith the folded IF copy, meaning only signal phase and amplitude areconsiderations. Further, no upconversion or downconversion is requiredsince cancellation may be performed without need for consideration offrequency.

As an example only, IF frequency for ELINT applications may be less thanabout 1 GHz, while corresponding RF frequency may be as high as 20 GHzor more. In one example for illustration purposes, an RF signal may havea frequency of about 10.4 GHz, and a sample rate of about 2 Gsps may beemployed to result in an IF frequency of about 400 MHz. As anotherexample for illustration purposes, an RF signal may have a frequency ofabout 130 MHz, and a sample rate of about 200 Msps may be employed toresult in an IF frequency of about 70 MHz.

Since the disclosed systems and methods may be implemented withoutup-conversion of the cancellation signal, errors introduced by theup-conversion process may be avoided, e.g., including phase noise andmis-match between desired frequency/phase and achieved mixerfrequency/phase. Further, the disclosed systems and methods may beimplemented without knowledge of the exact frequency of the signal to becancelled. Note that when up-converting the cancellation signal, anyfrequency estimation error can result in not just imperfectcancellation, but can even introduce an extra interferer (namely thecancellation signal itself). This embodiment provides the particularadvantage that the system complexity may be greatly reduced whilemaintaining good performance, thus the cost, size, weight, and power mayall be significantly reduced when compared to approaches relying onconventional technology.

In one exemplary embodiment of the disclosed systems and methods, theimpact of sample clock imperfections may be mitigated by using the sameclock for both the signal and cancel paths. In this regard, the sameclock may be employed to drive two system pulse-based samplers (i.e., asignal path sampler and a cancellation path sampler) so that the foldedIF signal is synchronized with the RF signal to meet the condition ofcanceling the RF signal at the sample instances. In another embodiment,a cancellation signal may be synchronized with the RF signal, forexample, by developing the cancellation signal using a bandpass samplingADC in the cancel path. In yet another exemplary embodiment, thedisclosed systems and methods may be implemented in conjunction with aNyquist folding receiver.

In one exemplary embodiment, an interference cancellation system may beprovided for cancellation of narrow band periodic interferers thatutilizes two RF samplers and two interpolation filters, with a first RFsampler and a first interpolation filter coupled in series within asignal path of the interference cancellation system, and with a secondRF sampler and a second interpolation filter coupled in series within acancel path of the interference cancellation system. The signal path andcancel path of the interface cancellation system may be fed with ananalog input RF signal. The IF output of the second interpolation filterof the cancel path may be fed back to the input of the first RF samplerof the signal path for cancellation after being delayed by a tunabletime delay. The folded frequency that is canceled depends on the timedelay, which may be tuned to control the frequency of the foldedcancelled signal, e.g., to achieve phase cancellation (rather thansignal inversion) so that the cancel path signal is 180 degrees out ofphase with the signal path signal and so that cancellation is phasedependent. All RF signals which fold to the same IF are cancelled, whichin effect generates a series of notches throughout the spectrum,allowing cancellation of an RF interferer with an IF signal without theneed to estimate the Nyquist zone. Although the cancellation may have afew other partial nulls, the majority of the band is still receivableand the average clock rate may be changed to cause the partial nulls andthe nulls in other Nyquist zones to move, without having to know whichNyquist zone the RF interferer is from that is being cancelled.

In one exemplary embodiment, the disclosed systems and methods may beemployed with changing clock rate, and the ability to track cancellationas RF sample rate changes may be provided by monitoring the interferencepower level and adapting the time delay (e.g., using adaptive time delaycircuitry) in a power minimization scheme (e.g., such as constrainedpower minimization). The ability to so track cancellation as RF samplerate changes may be enhanced when the RF sample rate changes smoothly.

The disclosed systems and methods may be implemented to provide asolution for single or multiple interfering source cancellation. In thecase of multiple source cancellation, the cancellation path may bemodified with a high dynamic range interference cancellation (HDRIC)path. In either case, no upconversion of the IF cancellation signal isrequired to cancel an RF interferer signal, but rather the IF signal(e.g., as output by a cancel path DAC) may be used to cancel the RFinterferer signal directly. Specifically, because pulse-based RFsampling is employed for the first stage of the interferencecancellation, it does not matter what the interference is doing betweensample points, which is unlike the case with a conventional ADC, wheresaturation between clocks will result in distortion or even saturationat sample time because of circuit hysteresis or other circuit memoryeffects. Thus, in the practice of the disclosed methods an RF interferersignal may be cancelled only at the sample times instead of everywhere,allowing RF cancellation using a folded version without upconversion ofthe IF cancellation signal.

In one respect, disclosed herein is an interference cancellation systemconfigured to receive an analog input RF signal, the interferencecancellation system including: cancel path circuitry including cancelpath signal sampling circuitry and signal isolation circuitry; andsignal path circuitry including signal path signal sampling circuitry.The cancel path signal sampling circuitry may be coupled to sample theanalog input RF signal to produce an analog or digital cancel pathselected sample IF signal, and the signal isolation circuitry may becoupled to receive the cancel path selected sample IF signal and toisolate a signal within the cancel path analog selected sample IF signaland to output the isolated signal as an analog cancellation IF signalhaving a different frequency than the analog input RF signal. The signalpath circuitry may be coupled to combine the analog input RF signal withthe analog cancellation IF signal to create a modified analog inputsignal, and the signal path signal sampling circuitry may be coupled tosample the modified analog input signal to produce a signal path analogor digital selected sample signal.

In another respect, disclosed herein is a method for cancelinginterference in an analog input RF signal, including: providing cancelpath circuitry including cancel path signal sampling circuitry andsignal isolation circuitry; providing signal path circuitry includingsignal path signal sampling circuitry; providing the analog input RFsignal to the signal path circuitry and the cancel path circuitry;utilizing the cancel path signal sampling circuitry to sample the analoginput RF signal to produce an analog or digital cancel path selectedsample IF signal; utilizing the signal isolation circuitry to isolate asignal within the analog or digital cancel path selected sample IFsignal and to output the isolated signal as an analog cancellation IFsignal having a different frequency than the analog input RF signal;combining the analog input RF signal with the analog cancellation IFsignal to create a modified analog input signal; and utilizing thesignal path signal sampling circuitry to sample the modified analoginput signal to produce a signal path analog or digital selected samplesignal.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a direct RF interference cancellation(DRIC) system as it may be configured according to one exemplaryembodiment of the disclosed systems and methods.

FIG. 2 illustrates a spectral example of a signal as it may be processedby a DRIC configured according to one embodiment of the disclosedsystems and methods.

FIG. 3 is a block diagram of a direct RF interference cancellation(DRIC) system as it may be configured according to another exemplaryembodiment of the disclosed systems and methods.

FIG. 4 shows simulation results corresponding to the direct RFinterference cancellation (DRIC) system embodiment of FIG. 3.

FIG. 5 shows simulation results corresponding to the direct RFinterference cancellation (DRIC) system embodiment of FIG. 3.

FIG. 6 is a block diagram of a direct RF interference cancellation(DRIC) system as it may be configured according to another exemplaryembodiment of the disclosed systems and methods.

FIG. 7 is a block diagram of a direct RF interference cancellation(DRIC) system as it may be configured according to another exemplaryembodiment of the disclosed systems and methods.

FIG. 8 is a block diagram of a Nyquist Folding RF interferencecancellation (DRIC) system as it may be configured according to anotherexemplary embodiment of the disclosed systems and methods.

FIG. 9 is a block diagram of a Nyquist Folding RF interferencecancellation (DRIC) system as it may be configured according to anotherexemplary embodiment of the disclosed systems and methods.

FIG. 10 is a block diagram of a Nyquist Folding RF interferencecancellation (DRIC) system as it may be configured according to anotherexemplary embodiment of the disclosed systems and methods.

FIG. 11 is a block diagram of a Nyquist Folding RF interferencecancellation (DRIC) system as it may be configured according to anotherexemplary embodiment of the disclosed systems and methods.

FIG. 12 is a block diagram of an cancellation system as it may beconfigured according to one exemplary embodiment of the disclosedsystems and methods.

FIG. 13 is a block diagram of cancel path signal sampling circuitry andcancel path signal isolation circuitry according to one exemplaryembodiment of the disclosed systems and methods.

DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

FIG. 1 illustrates a direct RF interference cancellation (DRIC) system100 as it may be configured according to one embodiment of the disclosedsystems and methods. As shown in FIG. 1, system 100 is configured toreceive an analog input radio frequency (RF) signal 150 (e.g., from a RFantenna or other suitable source) and to provide a digital selectedsample signal 162. Analog input RF signal 150 may include one or moredesired signals in the presence of one or more interferer signals. Inone embodiment, a DRIC system 100 may be employed to provideinterference cancellation for a reconfigurable direct RF receiver toallow significantly improved dynamic range over conventional methods.Examples of such reconfigurable direct RF receivers include thosereceiver systems described in U.S. patent application Ser. No.11/247,338 entitled “RECONFIGURABLE DIRECT RF BANDPASS SAMPLING RECEIVERAND RELATED METHODS,” filed on Oct. 11, 2005; and U.S. Pat. No.7,436,910 entitled “DIRECT BANDPASS SAMPLING RECEIVERS WITH ANALOGINTERPOLATION FILTERS AND RELATED METHODS,” each of the foregoingreferences being incorporated herein by reference in its entirety. Itwill be understood that the methodology of DRIC system 100 may beemployed for the conversion of a variety of types of electromagnetic andanalog signals to digital signals (e.g., radio frequency signals,optical signals, acoustic signals, etc.) in a variety of signalprocessing applications, e.g., digital receivers, communicationssystems, sonar, radar, high quality headsets, hearing devices, etc. Inthis regard, an “RF signal” as used herein includes any time domainwaveform that may be bandpass sampled.

FIG. 2 illustrates a spectral example (amplitude versus frequency) of asignal as it may be processed by DRIC system 100 according to oneexemplary embodiment. As shown in FIGS. 1 and 2, analog input RF signal150 includes RF interferer signal centered ƒ₁ and is first provided toanti-alias filter 102. In this exemplary embodiment, anti-alias filter102 may be any circuitry configuration that is tuned to filter outundesired frequencies of input signal 150 and to provide filtered analoginput RF signal 152 having a selected frequency range of interest asshown. Example circuitry that may be utilized for anti-alias filter 102includes, but is not limited to, bandpass filter, etc.

As shown in FIGS. 1 and 2, filtered analog input RF signal 152 isprovided to optional time delay circuitry 104 that may be implemented toprovide filtered analog input RF signal 152 as a delayed filtered RFsignal 154 to summer 106. Implementation of optional time delaycircuitry 104 allows for cancellation of non-periodic interferers andwill be described further herein. Optional time delay circuitry 104 isnot required for cancellation of periodic interferers. Filtered analoginput RF signal 152 is also provided through the feedback cancel path(shown in dashed line in FIG. 1) to summer 106. An optional non-zerotime delay T may be provided by time delay 104 to produce delayedfiltered analog input RF signal 154 that is time delayed relative tofiltered analog input RF signal 152 so that components of the cancelpath see the interferer signal present in analog input RF signal 150before signal path components downstream of summer 106. This time delayallows cancellation of the interferer signal (i.e., using analogcancellation IF signal 176) before the interferer signal is received bysignal path components downstream of summer 106 and provides for theability to cancel non-periodic interferers. Further information onfeedback cancellation processing may be found in U.S. Pat. No. 6,956,517and U.S. Pat. No. 7,091,894, each of which is incorporated herein byreference in its entirety. While this overall architecture is sometimesreferred to as a feedforward architecture, the term “feedback” is usedherein since portions of the cancellation may be controlled via feedbackloops.

Still referring to FIGS. 1 and 2, filtered analog input RF signal 152 ofthe cancel path (shown in dashed line in FIG. 1) may be stronglyattenuated (i.e., 10 dB up to 40 dB or more) by attenuator 114 toproduce attenuated filtered RF signal 164 so as to avoid saturation ofpulse-based cancel path RF sampler 116 of cancel path signal samplingcircuitry 182. Example circuitry that may be utilized for the cancelpath RF sampler circuitry 116 includes RF samplers from PICOSECOND PULSELABS (PSPL). Further information on configuration of RF sampler 116 andanti-alias filter 102 may be found in U.S. patent application Ser. No.11/247,338 entitled “RECONFIGURABLE DIRECT RF BANDPASS SAMPLING RECEIVERAND RELATED METHODS,” filed on Oct. 11, 2005; and U.S. Pat. No.7,436,910 entitled “DIRECT BANDPASS SAMPLING RECEIVERS WITH ANALOGINTERPOLATION FILTERS AND RELATED METHODS,” each of the foregoingreferences being incorporated herein by reference in its entirety.

As shown in FIG. 1, cancel path RF sampler 116 receives a sampling clock(Fs) input signal 190 b at a desired sampling frequency and performspulse-based sampling of attenuated filtered RF signal 164 basedthereupon. Sampling clock (Fs) input signal 190 b is synchronized withsampling clock (Fs) input signal 190 a that is provided to signal pathRF sampler 108 of signal path signal sampling circuitry 184 as shown.Sampling clock (Fs) signal 190 b determines the sampling frequency forthe cancel path RF sampler 116. This sampling clock (Fs) input signal190 b may be generated by sample clock circuit 128 (e.g., multi-clockgeneration circuitry) that is capable of generating two or more clocksignals that can be selected and used as sampling clocks (CLK1, CLK2 . .. ) for the sampling clock signal 190 b that is provided to cancel pathRF sampler 116. It is noted that sample clock circuit 128 could beimplemented using a wide variety of clock circuits. For example, thesample clock circuit 128 could be configured to always generate multipleclocks from which a sampling clock is selected. Alternatively, thesample clock circuit 128 could be configured to generate a single outputclock signal that is adjusted to provide a programmable clock outputsignal at the desired sampling frequency. Other variations could beprovided, as desired. It is also noted that in some embodiments a singleclock signal could be utilized, if desired. In such an implementation,the sample clock circuit 128 would provide a single fixed sampling clockoutput signal for the cancel path RF sampler 116.

Optional phase tuning circuitry 130 may be provided as shown, e.g., toallow minor alignment adjustments of the phase of sampling clock (Fs)signals 190 a and/or 190 b so as to provide better control overcancellation. For example, if sampling clock (Fs) signal 190 a is notexactly phase matched to sampling clock (Fs) signal 190 b, then thephase of sampling clock (Fs) signal 190 a may be adjusted to match thephase of sampling clock (Fs) signal 190 b (or vice-versa). Further, ifoptional time delay circuitry 104 is not as precise as required (e.g.,resulting in mis-match between the cancel path and signal path), thenclock phase of sampling clock (Fs) signals 190 a and/or 190 b may beadjusted to compensate for the lack of precision of time delay circuitry104. Examples of suitable phase tuning circuitry include, for example,voltage controlled time/phase delay circuits, etc.

As shown in FIG. 12, in one exemplary embodiment a single clock signalfrom sample clock circuit 128 may be split to provide sampling clock(Fs) input signals 190 a and 190 b, rather than providing andsynchronizing separate clock circuits as may be employed in anotherexemplary embodiment. Also shown in FIG. 12 are separate tunable delays1202 a and 1202 b that may be provided to perform the function of phasetune 130. It will be understood that sample clock circuit 128 and phasetuning circuitry 130 may be implemented in any other alternativecircuitry configuration suitable for generating sampling clock (Fs)input signals 190 a and 190 b including, for example, as a single sampleclock circuitry with integrated sample clock circuit and phase tuningcircuitry circuit components.

It is noted that provision of different clock signals allow forselection of an appropriate sampling clock based on meeting the Nyquistcriteria of the bandpass filter and based on criteria so as to avoidNyquist sampling problems due to Nyquist boundaries. Nyquist zones aredetermined by the sampling rate for the sampling circuitry 106, andNyquist criteria locate sampling zone boundaries at integer (K=0, 1, 2,3 . . . ) multiples of f_(s)/2 starting at DC (frequency=0 Hz). Inaddition, Nyquist zones alternate between non-inverted and invertedspectrums. Traditional Nyquist criteria states that for bandpasssampling, the sampling rate must be two-times or greater than thebandwidth of the signal frequency range of interest, and that forbaseband sampling, the sampling rate must be two-times or greater thanthe maximum frequency for the signal frequency range of interest.

As frequency ranges within the signal input spectrum are analyzed,depending upon the sampling frequency for the cancel path RF sampler116, one or more Nyquist boundaries could be crossed during processing.Thus, by having multiple sampling clock signals available, when aNyquist boundary for a first sampling clock signal is being reachedduring processing across a frequency range, a switch can be made tousing a second sampling clock signal. As such, the Nyquist boundary willalso change based upon this new sampling frequency. In operation,therefore, if anti-alias filter 102 is tuned to a new frequency and itsbandwidth includes a Nyquist boundary, a switch could be made to analternative sampling frequency so that reconstruction problems at theNyquist boundaries can be avoided. Thus, with proper selection of thesampling clock signals, the respective Nyquist zone boundaries for thesesampling clock frequencies can be made far enough apart so that Nyquistsampling problems for the first sampling clock can be avoided byswitching to the second sampling clock, and vice versa. In addition,more than two clock signals may be employed, and any number ofselectable clock signal frequencies could be provided, as desired. Itwill be understood that similar comments and methodology may be appliedto operation of signal path RF sampler 108 which is describedhereinbelow.

Still referring to FIGS. 1 and 2, analog sample RF signal 166 isprovided from cancel path RF sample circuitry 116 to image select filtercircuitry 118 of cancel path signal sampling circuitry 182. As shown,analog sample RF signal 166 includes multiple positive and negativefolded spectral images (repeating at ƒ_(s1), 2ƒ_(s1), etc.) obtained byconvolving attenuated filtered RF signal 164 in the frequency domain bya stream of impulses derived from sampling clock (Fs) input signal 190b. Image select filter circuitry 1118 may be, for example, a low passfilter, bandpass filter, or other circuitry that is suitable forselecting a desired folded image from the multiple folded images ofanalog sample RF signal 166, i.e., to select a desired positive imagecorresponding to an even Nyquist zone or to select a desired negativethat corresponds to an odd Nyquist zone. One particular example ofcircuitry that may be employed for image select filter circuitry 118include, but are not limited to, a low pass filter that is configured toselect the lowest frequency image from the multiple folded spectralimages of analog sample signal 166, or any other circuitry that issuitable for selecting all or part of a single Nyquist zone to form anIF signal image. Image select filter circuitry 118 then provides theselected folded image as analog selected sample IF signal 168 to cancelpath ADC circuitry 120 of cancel path signal sampling circuitry 182. ADCcircuitry 120 in turn Nyquist samples analog selected sample IF signal168 to produce a digital version of the selected folded image andprovides it as a digital selected sample IF signal 170 to digital signalprocessing (DSP) circuitry 122 of cancel path signal isolation circuitry180. As shown, cancel path signal isolation circuitry 180 in thisembodiment includes digital signal processing (DSP) circuitry 122, IFdigital to analog converter (DAC) 124, and amplifier circuitry 126.

In the practice of the disclosed systems and methods, cancel path ADC120 may be any circuitry (e.g., a single ADC device or combination ofdevices such as ADC device/s in combination with gain/attenuatordevice/s) suitable for analog to digital conversion. Examples ofsuitable ADC circuitry for cancel path ADC 120 include, but are notlimited to, successive approximation ADCs, flash ADCs, sample and holdADCs, sigma delta ADCs, composite ADCs, etc. It is also possible thatcancel path ADC 120 circuitry may be provided with noise shaping and/ortuning capability (e.g., a noise shaping tunable sigma-delta ADCdevice).

In the embodiment of FIGS. 1 and 2, DSP circuitry 122 is configured toisolate the interferer and remove the noise floor from digital selectedsample IF signal 170 (i.e., so as to reduce noise from the cancel pathgetting into the signal path after summation of cancel path and signalpath in summer 106) to produce processed digital cancel path IF signal172. DSP circuitry 122 may include, for example, an analysis filter bankfollowed by thresholding, then followed by zeroing out low amplitudefilters from the filter bank, and then followed by synthesis toreconstruct any interferers. Note that processed digital cancel path IFsignal 172 will be zero if there are no interferers present. However, ifat least one interferer is present, then processed digital cancel pathIF signal 172 will be the at least one interferer. Further, it will beunderstood that multiple interferers may be present in the cancel path,in which case processed digital cancel path IF signal 172 will includethe multiple interferers. Further information on interferencecancellation may be found in U.S. Pat. No. 6,956,517 and U.S. Pat. No.7,091,894, each of which is incorporated herein by reference in itsentirety.

Processed digital cancel path IF signal 172 is next provided as shown inFIG. 1 from DSP circuitry 122 to IF digital to analog converter (DAC)124 which converts processed digital cancel path IF signal 172 to analogcancel path IF signal 174. Examples of suitable DAC circuitry for IFdigital to analog converter (DAC) 124 include, but are not limited to,inverse sample and hold, interpolating, delta sigma, composite, etc. IFdigital to analog converter (DAC) 124 then provides analog cancel pathIF signal 174 to optional amplifier circuitry 126 which inverselyamplifies analog cancel path IF signal 174 to match amplitude of delayedfiltered RF signal 154, and outputs this inverse amplified signal asanalog cancellation IF signal 176. It will be understood that amplifiercircuitry 126 may be configured with pre-set values or may be configuredto be programmable in real time, e.g., to compensate for cancel pathand/or delay element gains or losses to properly match the amplitude ofthe cancellation signal 176 with delayed filtered RF signal 154 at theinput of the summer 106. Analog cancellation IF signal 176 is then addedto delayed filtered RF signal 154 (which may include both desiredsignal/s and interferer signal/s) by summer 106 to result in a modifiedanalog input signal 156 that, at the specific sample times determined bythe sample clock 190 a, includes any desired signal/s plus partially orcompletely cancelled interferer signal/s.

Still referring to FIG. 1, modified analog input signal 156 is providedfrom summer 106 to signal path RF sampler circuitry 108 where it ispulse-based sampled so as to result in a sampled analog signal 158 thatincludes multiple folded copies of the desired signal/s as shown in FIG.2. As shown in FIG. 1, signal path RF sampler 108 receives a samplingclock (Fs) input signal 190 a at a desired sampling frequency, and thatis synchronized with sampling clock (Fs) input signal 190 b aspreviously described. Sampling clock (Fs) signal 190 a determines thesampling frequency for the signal path RF sampler 108 and may begenerated by sample clock circuit 128 and optional phase tuningcircuitry 130 in a manner as previously described for sampling clock(Fs) signal 190 b such that pulsed-based sampling performed by signalpath RF sampler circuitry 108 is synchronized with pulse-based samplingperformed by cancel path RF sampler circuitry 116. As such, the sampletimes in sampled analog signal 158 are synchronized with (i.e., the sameas) the sample times in analog sample RF signal 166, with correction forany non-zero time delay T imparted by time delay circuitry 104.

As shown, sampled analog signal 158 is next provided to signal pathimage select filter circuitry 110 of signal path signal samplingcircuitry 184 that is configured to select the desired folded signalimage from the multiple folded signal copies of sampled analog signal158, and to output the desired signal image as an analog selected samplesignal 160. In this regard, signal path image select filter circuitry110 may be, for example, a low pass filter, a bandpass filter in thebaseband Nyquist zone, a bandpass filter selecting a higher Nyquistzone, etc. Analog selected sample signal 160 is then provided to signalpath ADC 112 which samples the desired signal, resulting in asubstantially clean digital image of the desired signal (e.g., withoutsaturation or other problems caused by strong interference) in digitalselected sample signal 162. DSP circuitry 122 may be configured tocontrol the phase inversion rather than using an inverting amplifier in126. Although not shown, interference cancellation may be monitored atthe output of signal path ADC 112, or alternatively at any othersuitable point in the signal path after signal path RF sampler circuitry108.

Still referring to FIG. 2, signal path ADC 112 component may be providedto include a similar or different type of analog to digital conversioncircuitry as does cancel path ADC component 120. For example, signalpath ADC 112 may be a traditional ADC device (e.g., successiveapproximation ADC device, flash ADC device, sample and hold ADC device,sigma-delta ADC device, etc.), a noise shaping tunable sigma-delta. ADCdevice, composite ADC device, including time-interleaved, etc. Similarto cancel path ADC 120, signal path ADC 112 may be any circuitry (e.g.,a single ADC device or combination of devices such as ADC device/s incombination with gain/attenuator device/s) suitable for analog todigital conversion. In such a case, signal path ADC 112 may becontrolled, for example, to optimize or hone in on a desired signal, toblock an interferer signal, etc. Advantages of direct RF interferencecancellation (DRIC) system 100 include flexible cancellation and ease ofhandling of multiple interferers or time varying interferers such aswideband chirp signals.

Referring again to FIG. 12, signal path signal sampling circuitry 184,cancel path signal sampling circuitry 182, and cancel path signalisolation circuitry 180 may be configured in different ways, with cancelpath signal sampling circuitry 182 providing a selected sample IF signal188 (which may be either digital IF signal 170 or analog IF signal 168as appropriate to the particular embodiment) to cancel path signalisolation circuitry 180, and with signal path signal sampling circuitry184 outputting a signal path selected sample signal 198 (which may beeither analog selected sample signal 160 or digital selected samplesignal 162 as appropriate to the particular embodiment). For example, incertain embodiments signal path signal sampling circuitry 184 may beconfigured to include signal path RF sampler 108 and image select filter110, and cancel path signal sampling circuitry 182 may be configured toinclude a cancel path RF sampler 116, cancel path image select filter118, and cancel path ADC 120 as shown in FIG. 1. In such an embodiment,cancel path signal isolation circuitry 180 may be configured to receivea digital selected sample IF signal 170 and may include DSP 122, IF DAC124 and amplifier 126. Alternatively, cancel path signal samplingcircuitry 182 may be configured to include a cancel path RF sampler 116and a cancel path image select filter 118, i.e., with no cancel pathADC. In such an embodiment, cancel path signal isolation circuitry 180may be configured to receive an analog selected sample IF signal 168,and may be configured to include a tunable filter 310 and amplifier 126as shown in FIG. 3. In yet another alternative shown in FIG. 13, cancelpath signal sampling circuitry 182 may be configured to include a directRF sampling ADC 186 that may be provided as a single circuitry componentthat performs the functions of separate RF sampler, image select, andADC circuitry components, i.e., with low pass filter but withoutseparate cancel path RF sampler and cancel path image select filtercomponents. In such an embodiment, cancel path signal isolationcircuitry 180 may be configured to receive a digital selected sample IFsignal 170 and may include DSP 122, IF DAC 124 and amplifier 126.

It will be understood that the various embodiments of direct RF samplercircuitry illustrated and described herein for either of the signal pathor cancel path may be interchanged for use in either a signal path orcancel path of a given DRIC system embodiment as long as the appropriatetype of selected sample IF signal (i.e., either digital or analog) isprovided in the cancel path by the selected type of cancel path signalsampling circuitry 182 to the selected type of cancel path signalisolation circuitry 180. With that proviso, cancel path signal samplingcircuitry 182 of any given DRIC system embodiment may be configured asshown in any one of FIG. 1, 3, or 13. Similarly, signal path signalsampling circuitry 184 of any given DRIC system may be configured in thesame manner (with identical or similar circuitry) as cancel path signalsampling circuitry 182 is configured in any one of FIG. 1, 3, or 13.However, in some applications it may be more desirable for signal pathsignal sampling circuitry 184 to be configured with a direct RF samplingADC (of the same type illustrated in cancel path of FIG. 13) when thedirect RF sampling ADC is not subject to hysteresis or other memoryeffects. In similar manner, cancel path signal isolation circuitry 180of any given DRIC system embodiment may be configured as shown forcancel path signal isolation circuitry 180 in either of FIG. 1 or 3, aslong as it receives the appropriate type of selected sample IF signal(i.e., either digital or analog) from the corresponding cancel pathsignal sampling circuitry 182 of the same embodiment.

FIG. 3 illustrates an alternate embodiment of a direct RF interferencecancellation (DRIC) system 300 as it may be configured according to thedisclosed systems and methods. The configuration of system 300 issimilar to the configuration of system 100 of FIG. 1, with the exceptionthat cancel path ADC 120, DSP 122, and IF DAC 124 of signal isolationcircuitry 180 are replaced with tunable filter circuitry 310 andassociated tunable filter control circuitry 312, along withdetect/measure/track interference circuitry 314 coupled to controltunable filter 310. Due to the absence of ADC, DSP and DAC in the cancelpath, the architecture of the embodiment of FIG. 3 may be implemented toprovide reduced power consumption and reduced cancel path latency (andhence reduced time delay requirement) as compared to the architecture ofthe embodiment of FIG. 1.

In the embodiment of FIG. 3, tunable filter circuitry 310 may becontrolled (e.g., by tuning control signals 332 provided by filtercontrol circuitry 312) to select an interferer signal frequency, or toblock out all signals in the absence of an interferer signal. Tunablefilter circuitry 310 then outputs the selected interferer signal asanalog cancel path IF signal 174. As shown, optionaldetect/measure/track interference circuitry 314 may be further providedto analyze at least one of analog selected sample IF signal 168 (viasignal path 320) and/or digital selected sample signal 162 (via signalpath 322) to identify an interferer signal frequency, and to provide aninterference frequency identity signal 330 (representative of theidentified interferer frequency) based thereupon to filter controlcircuitry 312. In this regard, signal path 320 may be employed to reactfaster to interference without waiting for the signal path to saturate.Signal path 322 may be employed without the need for an additional ADCat the output of signal path image select filter circuitry 110, and maybe employed in one exemplary embodiment in which cancel path tunablefilter circuitry 310 is combined with cancel path image select filtercircuitry 118. Filter control circuitry 312 in turn controls tunablefilter 310 to select the interferer signal frequency for analog cancelpath IF signal 174 based on interference frequency identity signal 320.Alternatively, detect/measure/track interference circuitry 314 may beabsent where the frequency of interference is known apriori. Since thefolded image of analog selected sample IF signal 168 is at IF instead ofa much higher frequency RF, and since the range of tunable filtercircuitry 310 is far smaller (only needing to cover a single Nyquistzone), the tunable filter notch may be much more tightly designed thanin a conventional RF tunable notch filter implementation for handlinginterference.

Example circuitry that may be utilized for the tunable filter circuitry310 includes tunable filter banks available from PARATEK. If desired,other tunable filter technologies could be utilized, such as tunableoptical Mach-Zehnder filter technology, tunable image rejection notchfilters, tunable bandpass filters based on active inductor technology,tunable filter that use thin film ferroelectric varactors to providevoltage controlled phase shifting, and tunable filters the use RFmicroelectromechanical systems (MEMS) technology.

Example circuitry for filter control circuitry 312 includesmicroprocessor/s. Example circuitry for detect/measure/trackinterference circuitry 314 includes time domain detector and frequencymeasure filter control, e.g., employing microprocessor for detector ofinterference frequency.

FIGS. 4 and 5 show the results of a Simulink/Matlab simulation thatcorresponds approximately to the embodiment shown in FIG. 3 (with thetunable filter control performed manually rather than automatically inthe Simulink simulation). FIG. 4 shows the time domain output for a caseof three signals—a very strong interferer at 4315 MHz, a signal ofinterest (SOI) at 4400 MHz, and a very weak SOI at 4870 MHz. The RFsample rate in this simulation is 2 GHz, so that the Nyquist zonebandwidth is 1 GHz. Thus the signals fold to the range of DC to 1 GHz(for the case of a low pass interpolation or image select filtercircuitry).

The top panel of FIG. 4 shows the RF interferer alone at 4315 MHz (solidline), cancel path (dashed line), RF interferer plus cancel path priorto RF sampling (dashed-dotted line), and result after signal path RFsampling (solid line with circles). Note that while the combinedRF+Cancel path (green dash dot) is not always zero, it is zero at the RFsample points. The bottom panel of FIG. 4 shows a first signal ofinterest (SOI) at 4400 MHz (solid line), cancel path (IC) (dashed line),RF interferer plus cancel path (IC) prior to RF sampling (dashed-dottedline), and result after signal path RF Sampling (solid line withcircles). Note that the cancel path is zero as expected since allsignals except IF signals correspond to a narrow band about 4300 MHz areblocked by tunable filter circuitry 310 in FIG. 3. The time domain viewof FIG. 4 illustrates that cancellation only needs to be achieved at thesample points when pulse-based sampling is employed, i.e., it does notmatter what the signal frequency values are between the sample aperturewindows. Moreover, sample points where cancellation of the RF interfereris achieved correspond to the folded IF version of the RF interfererwhen phase inverted.

FIG. 5 shows a frequency domain view of the same simulation as FIG. 4with cancel path on and off. The dashed line shows signal processingresults with no cancellation path, with the interferer clearly seen at315 MHz (i.e., folded from 4315 MHz to 315 MHz). A first and strongersignal of interest SOI may be seen at 400 MHz (i.e., folded from 4400MHz to 400 MHz). A second and weaker SOI is not readily discernable at870 MHz (i.e., folded from 4870 MHz to 870 MHz) and is almost hidden bythe third harmonic of the interferer. It should be noted that thissimulation does not have any noise, and that with noise, the SOIs wouldbe hidden. It should also be noted that the third harmonic of theinterferer is a simulation artifact caused by dynamic range limitationsof Simulink and that even with very small simulation time steps and highfidelity approximation, the strong SOI is distorted slightly. The solidline in FIG. 5 shows signal processing results with the cancellationpath active. As shown, with the cancel path active, the interferer isheavily suppressed and the harmonic distortion from the interferer is nolonger present, allowing the weaker SOI to be readily detected.

Note that in any sort of active cancellation system, the cancellationpath must have enough dynamic range to handle the strong interferencesince the cancel signal needs to be approximately as strong as theinterfering signal. Using the disclosed systems and methods, thebandwidth of the cancel path may be half of the RF sample rate (e.g., 1GHz in the example shown in FIG. 5). This is far less total RF rangethan the RF input range, and achieving the high 3^(rd) order intercepton the IF amplifier in the cancel path is far easier than achieving ahigh 3^(rd) order intercept on a wideband RF amplifier and/orup-conversion mixer that would be required in a conventionalarchitecture that does not use the folded IF for cancellation.

FIG. 6 illustrates an alternate embodiment of a direct RF interferencecancellation (DRIC) system 600 as it may be configured according to thedisclosed systems and methods for periodic interference cancellationsuch as for narrowband sinusoidal interferers. The configuration ofsystem 600 is similar to the configuration of system 100 of FIG. 1, withthe exception that there is no time delay in the signal path. In theembodiment of FIG. 6, no time delay is required because cancellation maybe performed using any cycle of the interference. Because theinterference is periodic, phase control (e.g., using phase tuningcircuitry 130) may be employed to control pulse-based sampling ofattenuated filtered RF signal 164 in order to achieve phase inversionbetween the cancel path and signal path sampling. In this regard, thecancel path and sample path may be sampled 180 degrees out of phase witheach other (or may be sampled at the same phase and then invertedrelative to each other) so that the interferer/s in the cancel path is180 degrees out of phase with the interferer/s in filtered analog inputRF signal 152, thus achieving cancellation of the interferer/s ratherthan requiring negating the cancellation path with amplifier circuitry126. Thus, note that amplifier circuitry 126 is denoted by “G” ratherthan “−G” in FIG. 6.

FIG. 7 illustrates an alternate embodiment of a direct RF interferencecancellation (DRIC) system 700 as it may be configured according to thedisclosed systems and methods for periodic interference cancellation.The configuration of system 300 is similar to the configuration ofsystem 300 of FIG. 3, with the exception that there is no time delay inthe signal path, for the same reason as described in relation to FIG. 6.Further, like the embodiment of FIG. 6, phase control of cancel pathsampling may be employed rather than negating the cancellation path.

FIG. 8 illustrates an embodiment of a Nyquist Folding RF interferencecancellation (DRIC) system 800 as it may be configured according to thedisclosed systems and methods to utilize Nyquist folded bandpasssampling. The configuration of system 800 is similar to theconfiguration of system 100 of FIG. 1, with the exception that analoginput RF signal 150 is first passed through wideband pre-select filter802, and sample clock input signals 190 a and 190 b are generated byfrequency modulated RF clock circuit 804 to control signal path samplingby signal path RF sampler 108 and cancel path sampling by cancel path RFsampler 116, respectively. In this exemplary embodiment, the widebandpre-select filter 802 may have a center frequency within a frequencyrange of interest and having a bandwidth less than or equal to thefrequency range of interest and wide enough to cover multiple Nyquistzones, and the frequency modulated RF clock circuit 804 may beconfigured to provide non-uniform sampling for signals within themultiple Nyquist zones to induce frequency modulation on signalsdependent on a Nyquist zone of origin.

In operation of the embodiment of FIG. 8, multiple Nyquist zones arepassed through wideband preselect filter 802 and are allowed to fold ontop of each other during sampling by signal path RF sampler 108 andcancel path RF sampler 116. Because the sample clock input signals 190 aand 190 b are modulated, separate frequency modulations can be inducedwithin each Nyquist zone, and when the Nyquist zones fold on top of eachother, the different signals from different Nyquist zones can beseparated and identified based on the fact that the added modulation isdifferent for each Nyquist zone, i.e., since sample clock input signals190 a and 190 b are modulated the signals that are folded together fromdifferent Nyquist zones may be identified and distinguished. Thus, byusing one or more clock modulations to induce frequency modulations thatare Nyquist zone dependent (i.e., separate modulations are inducedwithin each Nyquist zone), multiple Nyquist zones can be aliasedtogether while still allowing for signals from different Nyquist zonesto be separated and identified based on the fact that the inducedmodulation is different for each Nyquist zone. Because the inducedmodulations can be measured, a determination can be made withoutambiguity of the Nyquist zone from which each signal originated.

Referring in more detail to the exemplary embodiment of FIG. 8, widebandpre-select filter 802 may be an ultra wideband (UWB) filter having abandwidth that is wide enough to pass multiple Nyquist zones where theNyquist zones are determined by the average RF sampling clockfrequencies for the signal path RF sampler 108 and cancel path RFsampler 116. Frequency modulated RF clock circuit 804 provides sampleclock input signals 190 a and 190 b to samplers 108 and 116,respectively that are not constant and that are adjusted or modulatedduring sampling. For example, the modulation may be a chirped sampleclock signal, although other types of modulated clock signals could alsobe used depending upon the results desired (e.g., a linear sawtoothmodulation, a sinusoidal modulation, a triangle modulation, a frequencyshift key modulation, a frequency agile modulation, a communicationsfrequency modulation, or a combination thereof). Other example modulatedclock signals and combinations of modulations may also be used toprovide non-uniform sampling including, but are not limited to,frequency shift key, frequency agile, phase shift, general frequencymodulation, etc. An ability to track interference cancellation as the RFsample rate changes may be provided by monitoring the interference powerlevel and adapting the time delay in a power minimization scheme (e.g.,such as power constrained). The ability to so track cancellation as RFsample rate changes may be enhanced when the RF sample rate changessmoothly.

In one example implementation, the wideband pre-select filter circuitry802 may be configured to have a bandwidth of about 20 GHz or more, andthe modulated sample clock input signals 190 a and 190 b may each begenerated to have an average sampling rate of about 2 GHz or more. Otherimplementations may be made, as desired. Further, wideband pre-selectfilter circuitry 802 may be tunable and or reconfigurable, e.g., in thecase where wideband pre-select filter circuitry 802 selects sub-regions,it may be advantageous to tune the sub-regions to cover different areasin response to jammers or to time-varying frequency regions of interest.It is also noted that the clock modulation may be switchable orotherwise reconfigurable. For example, it may be advantageous to changethe clock modulation from one type of modulation to another type ofmodulation in order to improve the performance against different classesof signals.

Thus, a single clock modulation, or multiple clock modulations,mathematically translate into different signal modulations dependingupon the Nyquist zone in which the signals are located before beingfolded together thereby allowing separation of the aliased signals anddetermination of the Nyquist zone from which they came. It is furthernoted that the frequency modulated sample clock input signals may betunable or switchable such that the center frequency of the sample clockinput signals 190 a and/or 190 b may be tuned to a desired frequencyand/or one of a plurality of generated clock signals may be selected. Inaddition, frequency modulated RF sampling clock 804 may be configuredsuch that the modulation for frequency modulated RF sampling clock 804is adjusted during operation of a receiver. Other variations andimplementations could also be utilized, if desired. Further informationon Nyquist folded bandpass sampling may be found in U.S. Pat. No.7,436,912; and U.S. Pat. No. 7,436,911, each of which is incorporatedherein by reference in its entirety.

Still referring to the embodiment of FIG. 8, tune delay circuitry 806(e.g., such as employed for tunable RF delay circuitry) is provided asshown to allow delay of modulated sample clock input signal 190 arelative to modulated sample clock input signal 190 b (or vice versa) toaccount for the propagation time difference between the first signalpath from output of wideband pre select filter 802 to input of signalpath RF sampler 108 and the second signal path from output of widebandpre select filter 802 to input of cancel path RF sampler 116. In thisregard, the tune delay 806 is employed in this embodiment to align thetime-varying clocks 190 a and 190 b so that they sample the waveform atthe same relative points in phase.

FIG. 9 illustrates another alternate embodiment of a Nyquist Folding RFinterference cancellation (DRIC) system 900 as it may be configuredaccording to the disclosed systems and methods to utilize Nyquist foldedbandpass sampling. The configuration of system 900 is similar to theconfiguration of system 800 of FIG. 8, with the exception that cancelpath ADC 120, DSP 122, and IF DAC 124 are replaced with tunable filtercircuitry 310 and associated tunable filter control circuitry 312 in amanner similar to the embodiment of FIG. 3. Also, similar to theembodiment of FIG. 3, detect/measure/track interference circuitry 314 isprovided and coupled to control tunable filter 310.

FIG. 10 illustrates another alternate embodiment of a Nyquist Folding RFinterference cancellation (DRIC) system 1000 as it may be configuredaccording to the disclosed systems and methods to utilize Nyquist foldedbandpass sampling for periodic interference cancellation. Theconfiguration of system 1000 is similar to the configuration of system800 of FIG. 8, with the exception that there is no time delay in thesignal path. In the embodiment of FIG. 10, no time delay is requiredbecause cancellation may be performed by inverting the cancellationsignal within DSP 122. With regard to the Nyquist Folding RFinterference cancellation embodiment of FIG. 9, inversion is notaccomplished by simple time delay even for periodic interferers becausethe interference has an induced modulation bandwidth at the input of thetunable filter 310 and a time delay will only cancel a single frequencycomponent (although partial cancellation may be obtained using timedelay rather than full signal inversion).

FIG. 11 illustrates another alternate embodiment of a Nyquist Folding RFinterference cancellation (DRIC) system 1100 as it may be configuredaccording to the disclosed systems and methods to utilize Nyquist foldedbandpass sampling. The configuration of system 1100 is similar to theconfiguration of system 800 of FIG. 8, with the exception that there isno time delay in the signal path. In the embodiment of FIG. 11, thecancel path ADC 120, DSP 122, and IF DAC 124 are replaced with tunablefilter circuitry 310 and associated tunable filter control circuitry 312in a manner similar to the embodiments of FIGS. 3 and 9. Also, similarto the embodiments of FIGS. 3 and 9, detect/measure/track interferencecircuitry 314 is provided and coupled to control tunable filter 310.

Where it is desirable to provide amplification, it will be understoodthat one or more low noise amplifiers (LNAs) and/or IF amplifiers and/ornarrow band filters may be employed in any of the system configurationsdescribed and illustrated herein.

While the invention may be adaptable to various modifications andalternative forms, specific embodiments have been shown by way ofexample and described herein. However, it should be understood that theinvention is not intended to be limited to the particular formsdisclosed. Rather, the invention is to cover all modifications,equivalents, and alternatives falling within the spirit and scope of theinvention as defined by the appended claims. Moreover, the differentaspects of the disclosed systems and methods may be utilized in variouscombinations and/or independently. Thus the invention is not limited toonly those combinations shown herein, but rather may include othercombinations.

1. An interference cancellation system configured to receive an analoginput RF signal, said interference cancellation system comprising:cancel path circuitry comprising cancel path signal sampling circuitryand signal isolation circuitry; and signal path circuitry comprisingsignal path signal sampling circuitry; wherein said cancel path signalsampling circuitry is coupled to sample said analog input RF signal toproduce an analog or digital cancel path selected sample IF signal, andwherein said signal isolation circuitry is coupled to receive saidcancel path selected sample IF signal and to isolate a signal withinsaid cancel path analog selected sample IF signal and to output saidisolated signal as an analog cancellation IF signal having a differentfrequency than said analog input RF signal; and wherein said signal pathcircuitry is coupled to combine said analog input RF signal with saidanalog cancellation IF signal to create a modified analog input signal,wherein said signal path signal sampling circuitry is coupled to samplesaid modified analog input signal to produce a signal path analog ordigital selected sample signal.
 2. The system of claim 1, wherein saidcancel path signal sampling circuitry comprises cancel path RF samplercircuitry and cancel path image select filter circuitry; wherein saidsignal path signal sampling circuitry comprises signal path RF samplercircuitry and signal path image select filter circuitry; wherein saidcancel path RF sampler circuitry is coupled to sample said analog inputRF signal to produce a cancel path sampled analog signal includingmultiple folded signal images of at least a portion of said analog inputRF signal, wherein said cancel path image select filter circuitry iscoupled to receive said cancel path analog sample RF signal and toselect a desired folded signal image from said multiple folded signalcopies of said cancel path analog sample RF signal, wherein said cancelpath signal sampling circuitry is configured to output said selecteddesired signal image as said analog or digital cancel path selectedsample IF signal, and wherein said signal isolation circuitry is coupledto receive said cancel path analog or digital cancel path selectedsample IF signal and to isolate a signal within said cancel path analogor digital cancel path selected sample IF signal and to output saidisolated signal as an analog cancellation IF signal having a differentfrequency than said analog input RF signal; and wherein said signal pathcircuitry is coupled to combine said analog input RF signal with saidanalog cancellation IF signal to create a modified analog input signal,wherein said signal path RF sampler circuitry is coupled to sample saidmodified analog input signal to produce a signal path sampled analogsignal including multiple folded signal images of at least a portion ofsaid modified analog input signal, and wherein said signal path imageselect filter circuitry is coupled to receive said signal path sampledanalog signal and to select a desired folded signal image from saidmultiple folded signal copies of said signal path sampled analog signaland to output said selected desired signal image as a signal path analogselected sample signal.
 3. The system of claim 2, wherein said analoginput RF signal comprises at least one desired signal in the presence ofat least one interfering signal; wherein said cancel path analog sampleRF signal includes multiple folded signal images of said interferingsignal and at least a portion of said desired signal; wherein saidcancel path analog or digital cancel path selected sample IF signalincludes a selected folded signal image of said interfering signal andat least a portion of said desired signal; wherein said analogcancellation IF signal includes said interfering signal in the absenceof said desired signal and is effective to at least partially cancelsaid at least one interfering signal in said analog input RF signal whencombined with said analog input RF signal by said signal path circuitryso as to produce said modified analog input signal; and wherein saidmodified analog input signal includes at least a portion of said desiredsignal.
 4. The system of claim 3, further comprising anti-alias filtercircuitry coupled to filter out one or more frequencies of said analoginput RF signal prior to said signal path circuitry and said cancel pathcircuitry.
 5. The system of claim 3, wherein said signal path circuitryfurther comprises time delay circuitry coupled to delay said analoginput RF signal prior to combining said analog input RF signal with saidanalog cancellation IF signal to create said modified analog inputsignal, said time delay circuitry configured to delay said analog inputRF signal for a period of time that is sufficient to allow said analogcancellation IF signal to be provided and combined with said analoginput RF signal so as to at least partially cancel said at least oneinterfering signal in said analog input RF signal and produce saidmodified analog input signal.
 6. The system of claim 3, wherein said atleast one interfering signal is a periodic signal; wherein said signalpath circuitry and said cancel path circuitry is configured such thatsaid analog input RF signal is not delayed prior to combining saidanalog input RF signal with said analog cancellation IF signal to createsaid modified analog input signal; and wherein said interferencecancellation circuitry further comprises phase tuning circuitry coupledto control sampling of at least one of said signal path RF samplercircuitry or said cancel path RF sampler circuitry to achieve phaseinversion between said cancel path sampling and said signal pathsampling such that said analog cancellation IF signal at least partiallycancels said at least one interfering signal in said analog input RFsignal when said analog cancellation IF signal is combined with saidanalog input RF signal to produce said modified analog input signal. 7.The system of claim 3, wherein said cancel path signal samplingcircuitry further comprises cancel path analog to digital converter(ADC) circuitry; wherein said cancel path signal isolation circuitrycomprises digital signal processing (DSP) circuitry, IF digital toanalog converter (DAC) circuitry, and amplifier circuitry; wherein saidcancel path ADC circuitry is coupled to produce a digital selectedsample IF signal including said interfering signal and said at least aportion of said desired signal; wherein said DSP circuitry is coupled toreceive said digital selected sample IF signal and to isolate saidinterfering signal to produce a processed digital cancel path IF signalincluding said interfering signal in the absence of said desired signal;wherein said IF DAC circuitry is configured to convert said processeddigital cancel path IF signal to an analog cancel path IF signal; andwherein said amplifier circuitry is configured to inversely amplify saidanalog cancel path IF signal to substantially match an amplitude of saidanalog input RF signal to produce said analog cancellation IF signal. 8.The system of claim 3, wherein said cancel path RF sampler circuitry isconfigured to produce an analog selected sample IF signal; wherein saidsignal isolation circuitry comprises tunable filter circuitry andamplifier circuitry; wherein said tunable filter circuitry is coupled toreceive said analog selected sample IF signal and is controlled toselectably pass said interfering signal frequency in the absence of saiddesired signal to produce said analog cancel path IF signal; and whereinsaid amplifier circuitry is configured to amplify said analog cancelpath IF signal to substantially match an amplitude of said analog inputRF signal to produce said analog cancellation IF signal.
 9. The systemof claim 3, further comprising at least one sample clock circuit coupledto synchronize said sampling performed by said signal path RF samplercircuitry with said sampling performed by said cancel path RF samplercircuitry.
 10. The system of claim 3, further comprising modulatedfrequency clock circuitry and wideband filter circuitry; said frequencymodulated RF clock circuitry coupled to control sampling by each of saidsignal path RF sampler circuitry and said cancel path RF samplercircuitry to provide non-uniform sampling for signals within multipleNyquist zones to induce frequency modulation on signals dependent on aNyquist zone of origin; and said wideband filter circuitry coupled tofilter said analog input RF signal prior to said signal path circuitryand said cancel path circuitry, said wideband filter circuitry having acenter frequency within a frequency range of interest and having abandwidth less than or equal to the frequency range of interest and wideenough to cover multiple Nyquist zones associated with said modulatedfrequency clock.
 11. The system of claim 3, further comprising signalpath analog to digital converter (ADC) circuitry coupled to sample saiddesired signal in said signal path analog selected sample signal toproduce a substantially clean digital image of said desired signal in adigital output signal.
 12. The system of claim 1, wherein said cancelpath signal sampling circuitry comprises direct RF sampling ADCcircuitry; wherein said signal path signal sampling circuitry comprisessignal path RF sampler circuitry and signal path image select filtercircuitry; wherein said cancel path signal isolation circuitry comprisesdigital signal processing (DSP) circuitry, IF digital to analogconverter (DAC) circuitry, and amplifier circuitry; wherein said cancelpath direct RF sampling ADC circuitry is coupled to produce a digitalselected sample IF signal including said interfering signal and said atleast a portion of said desired signal; wherein said DSP circuitry iscoupled to receive said digital selected sample IF signal and to isolatesaid interfering signal to produce a processed digital cancel path IFsignal including said interfering signal in the absence of said desiredsignal; wherein said IF DAC circuitry is configured to convert saidprocessed digital cancel path IF signal to an analog cancel path IFsignal; and wherein said amplifier circuitry is configured to inverselyamplify said analog cancel path IF signal to substantially match anamplitude of said analog input RF signal to produce said analogcancellation IF signal; and wherein said signal path is coupled tocombine said analog input RF signal with said analog cancellation IFsignal to create a modified analog input signal, wherein said signalpath RF sampler circuitry is coupled to sample said modified analoginput signal to produce a signal path sampled analog signal includingmultiple folded signal images of at least a portion of said modifiedanalog input signal, and wherein said signal path image select filtercircuitry is coupled to receive said signal path sampled analog signaland to select a desired folded signal image from said multiple foldedsignal copies of said signal path sampled analog signal and to outputsaid selected desired signal image as a signal path analog selectedsample signal.
 13. A method for canceling interference in an analoginput RF signal, comprising: providing cancel path circuitry comprisingcancel path signal sampling circuitry and signal isolation circuitry;providing signal path circuitry comprising signal path signal samplingcircuitry; providing said analog input RF signal to said signal pathcircuitry and said cancel path circuitry; utilizing said cancel pathsignal sampling circuitry to sample said analog input RF signal toproduce an analog or digital cancel path selected sample IF signal;utilizing said signal isolation circuitry to isolate a signal withinsaid analog or digital cancel path selected sample IF signal and tooutput said isolated signal as an analog cancellation IF signal having adifferent frequency than said analog input RF signal; combining saidanalog input RF signal with said analog cancellation IF signal to createa modified analog input signal; and utilizing said signal path signalsampling circuitry to sample said modified analog input signal toproduce a signal path analog or digital selected sample signal.
 14. Themethod of claim 13, wherein said cancel path signal sampling circuitrycomprises cancel path RF sampler circuitry and cancel path image selectfilter circuitry; wherein said signal path signal sampling circuitrycomprises signal path RF sampler circuitry and signal path image selectfilter circuitry; and wherein said method further comprises: providingcancel path circuitry comprising cancel path RF sampler circuitry,cancel path image select filter circuitry, and signal isolationcircuitry; providing signal path circuitry comprising signal path RFsampler circuitry and signal path image select filter circuitry;providing said analog input RF signal to said signal path circuitry andsaid cancel path circuitry; utilizing said cancel path RF samplercircuitry to sample said analog input RF signal to produce a cancel pathanalog sample RF signal including multiple folded signal images of atleast a portion of said analog input RF signal; utilizing said cancelpath image select filter circuitry to select a desired folded signalimage from said multiple folded signal copies of said cancel path analogsample RF signal and outputting said selected desired signal image fromsaid cancel path signal sampling circuitry as said analog or digitalcancel path selected sample IF signal; utilizing said signal isolationcircuitry to isolate a signal within said analog or digital cancel pathselected sample IF signal and to output said isolated signal as ananalog cancellation IF signal having a different frequency than saidanalog input RF signal; combining said analog input RF signal with saidanalog cancellation IF signal to create a modified analog input signal;utilizing said signal path RF sampler circuitry to sample said modifiedanalog input signal to produce a signal path sampled analog signalincluding multiple folded signal images of at least a portion of saidmodified analog input signal; and utilizing said signal path imageselect filter circuitry to select a desired folded signal image fromsaid multiple folded signal copies of said signal path sampled analogsignal and to output said selected desired signal image as a signal pathanalog selected sample signal.
 15. The method of claim 14, wherein saidanalog input RF signal comprises at least one desired signal in thepresence of at least one interfering signal; wherein said cancel pathanalog sample RF signal includes multiple folded signal images of saidinterfering signal and at least a portion of said desired signal;wherein said cancel path analog or digital cancel path selected sampleIF signal includes a selected folded signal image of said interferingsignal and at least a portion of said desired signal; wherein saidanalog cancellation IF signal includes said interfering signal in theabsence of said desired signal; and wherein said method furthercomprises at least partially canceling said at least one interferingsignal in said analog input RF signal by combining said analogcancellation IF signal with said analog input RF signal to produce saidmodified analog input signal, said modified analog input signalincluding at least a portion of said desired signal.
 16. The method ofclaim 15, further comprising providing and utilizing anti-alias filtercircuitry to filter out one or more frequencies of said analog input RFsignal prior to providing said analog input RF signal to said signalpath circuitry and said cancel path circuitry.
 17. The method of claim15, further comprising providing and utilizing time delay circuitry todelay said analog input RF signal prior to combining said analog inputRF signal with said analog cancellation IF signal to create saidmodified analog, input signal, a value of said time delay beingsufficient to allow said analog cancellation IF signal to be providedand combined with said analog input RF signal so as to at leastpartially cancel said at least one interfering signal in said analoginput RF signal and produce said modified analog input signal.
 18. Themethod of claim 15, wherein said at least one interfering signal is aperiodic signal; wherein said analog input RF signal is not delayed bytime delay circuitry prior to combining said analog input RF signal withsaid analog cancellation IF signal to create said modified analog inputsignal; and wherein said method further comprises providing andutilizing phase tuning circuitry to control said sampling of at leastone of said signal path RF sampler circuitry or said cancel path RFsampler circuitry to achieve phase inversion between said cancel pathsampling and said signal path sampling such that said analogcancellation IF signal at least partially cancels said at least oneinterfering signal in said analog input RF signal when said analogcancellation IF signal is combined with said analog input RF signal toproduce said modified analog input signal.
 19. The method of claim 15,wherein said cancel path signal sampling circuitry further comprisescancel path analog to digital converter (ADC) circuitry; wherein saidcancel path signal isolation circuitry comprises digital signalprocessing (DSP) circuitry, IF digital to analog converter (DAC), andamplifier circuitry; and wherein said method further comprises:utilizing said cancel path ADC circuitry to produce a digital selectedsample IF signal from said analog selected sample IF signal, saiddigital selected sample IF signal including said interfering signal andsaid at least a portion of said desired signal; utilizing said DSPcircuitry to isolate said interfering signal and produce a processeddigital cancel path IF signal from said digital selected sample IFsignal, said processed digital cancel path IF signal including saidinterfering signal in the absence of said desired signal; utilizing saidIF DAC circuitry to convert said processed digital cancel path IF signalto an analog cancel path IF signal; and utilizing said amplifiercircuitry to produce said analog cancellation IF signal by inverselyamplifying said analog cancel path IF signal to substantially match anamplitude of said analog input RF signal.
 20. The method of claim 15,wherein said signal isolation circuitry comprises tunable filtercircuitry and amplifier circuitry; and wherein said method furthercomprises: utilizing said cancel path RF sampler circuitry to produce ananalog selected sample IF signal; providing said analog selected sampleIF signal to said tunable filter circuitry and controlling said tunablefilter circuitry to selectably pass said interfering signal frequency inthe absence of said desired signal to produce said analog cancel path IFsignal; and utilizing said amplifier circuitry to produce said analogcancellation IF signal by amplifying said analog cancel path IF signalto substantially match an amplitude of said analog input RF signal. 21.The method of claim 15, further comprising providing and utilizing atleast one sample clock circuit to generate sampling clock signals tosynchronize said sampling performed by said signal path RF samplercircuitry with said sampling performed by said cancel path RF samplercircuitry.
 22. The method of claim 15, further comprising: providingmodulated frequency clock circuitry and wideband filter circuitry;utilizing said frequency modulated RF clock circuitry to controlsampling by each of said signal path RF sampler circuitry and saidcancel path RF sampler circuitry to provide non-uniform sampling forsignals within multiple Nyquist zones to induce frequency modulation onsignals dependent on a Nyquist zone of origin; and utilizing saidwideband filter circuitry to filter said analog input RF signal prior toproviding said analog input RF signal to said signal path circuitry andsaid cancel path circuitry, said wideband filter circuitry having acenter frequency within a frequency range of interest and having abandwidth less than or equal to the frequency range of interest and wideenough to cover multiple Nyquist zones associated with said modulatedfrequency clock.
 23. The method of claim 15, further comprisingproviding and utilizing a signal path analog, to digital converter (ADC)circuitry to sample said desired signal in said signal path analogselected sample signal to produce a substantially clean digital image ofsaid desired signal in a digital output signal.
 24. The method of claim13, wherein said cancel path signal sampling circuitry comprises directRF sampling ADC circuitry; wherein said cancel path signal isolationcircuitry comprises digital signal processing (DSP) circuitry, IFdigital to analog converter (DAC), and amplifier circuitry; and whereinsaid method further comprises: utilizing said cancel path direct RFsampling ADC circuitry to produce a digital selected sample IF signalincluding said interfering signal and said at least a portion of saiddesired signal; utilizing said DSP circuitry to isolate said interferingsignal and produce a processed digital cancel path IF signal from saiddigital selected sample IF signal, said processed digital cancel path IFsignal including said interfering signal in the absence of said desiredsignal; utilizing said IF DAC circuitry to convert said processeddigital cancel path IF signal to an analog cancel path IF signal; andutilizing said amplifier circuitry to produce said analog cancellationIF signal by inversely amplifying said analog cancel path IF signal tosubstantially match an amplitude of said analog input RF signal.